William Penn Building
109 Chesley Drive
Media, PA 19063

Avoid Power Surges from Lightning


Lightning-related property damage has soared by 83 percent since 2004, according to insurance industry data. Damage to valuable electronics such as flat panel televisions have helped drive up insured losses, which totaled more than $1 billion in 2010.

Additionally, hundreds of deaths and injuries are linked to lightning strikes each year, according to the National Weather Service. Seeking shelter early is the most effective protection against a lightning strike.

As electronics have become more sophisticated and commonplace in homes and businesses, costs associated with lightning-related losses have risen. The number of paid insurance claims for lightning damage rose 12.8 percent from 2009 to 2010, and the average claim amount increased from $4,296 to $4,846, according to the Insurance Information Institute.

Unlike other natural hazards that affect specific regions of the country, numerous states are exposed to lightning. While some areas, such as Alabama, Florida, Mississippi, Louisiana, North Carolina, South Carolina and Texas have more frequent lightning, it can strike anywhere if the weather conditions are right so it is important for everyone to understand their lightning risk.

Lightning does not need to actually directly strike a home or business to induce a power surge and cause extensive damage. While often lasting only a millisecond, power surges can raise the voltage in electronic circuits from a few hundred to as much as several thousand volts. They are one of the most severe, common and immediate dangers to modern, sensitive electronic equipment. The resulting damage can range from loss of expensive electronic equipment to structure fires. Lightning protection systems are designed to protect a structure and provide a specified path to harness and safely ground the super-charged current of the lightning bolt. The system receives and routes the electrical strike into the earth, thereby discharging it and eliminating the danger.

In conjunction with Lightning Safety Awareness Week, which is June 24-30, the Insurance Institute for Business & Home Safety (IBHS) provides the following important information about reducing the risk of lightning-related property damage.

IBHS recommends that properties in areas subject to an average flash density of 2 to 3 fl/sq km/yr or greater, as defined in the map shown below, should have a lightning protection system installed. An effective option is the installation of surge protection on the electrical service to the property.


• For protection from lightning strikes in the general area of your home and externally produced surge, a whole-house surge protector is the best starting point for reducing the risk of damage or a fire. It is important to make sure that it is either a secondary surge arrestor tested to IEEE C62.11 or a transient voltage suppressor that has been tested to UL 1449, 2nd Edition. Many utility companies provide these systems.

• The protector should be installed in accordance with Article 280 or Article 285 of the National Electrical Code (as is applicable) and must have a working indicator light. Consider installing additional protection for important or expensive electronic equipment, which should include localized surge protection for power cords to the electronic equipment and any telephone and cable/satellite TV lines connecting to the equipment.

• Whole house surge protection will not protect you from a direct strike on your house. For added protection from a direct strike, add receptors on the roof and cables that will help to direct the strike away from the interior of your house. Homes in areas subject to an average flash density of 10 to 14 fl/sq km/yr or greater as shown on the accompanying map have an increased exposure to lightning. Homeowners in these areas should consider installing protection from a direct strike in addition to whole-house surge protection.


Lightning protection systems are designed to protect a structure and provide a specified path to harness and safely ground the super-charged current of the lightning bolt. The system works by receiving the strike and routing it harmlessly into the ground thus discharging the dangerous electrical event. For more information on lightning protection systems, see FM Global Property Loss Prevention Data Sheet 5-11 -Lightning and Surge Protection for Electrical Systems, available at http://fmglobal.com.

Lightning protection systems should be designed and installed in accordance with:

• National Fire Protection Assoc. (NFPA) 780, Standard for the Installation of Lightning Protection Systems

• Underwriters’ Laboratories, Inc. (UL) Standard 96A, Installation Requirements for Lightning Protection Systems

• Lightning Protection Institute (LPI) Standard 175, Standard of Practice for the Design – Installation – Inspection of Lightning Protection Systems

• All materials should comply in weight, size, and composition with the requirements of the UL 96 Materials Standards.

• All equipment should be UL listed and properly labeled.

• Equipment should be the manufacturer’s latest approved design of construction to suit the application where it is to be used in accordance with accepted industry standards and with NFPA, LPI, & UL requirements.


Many areas with lightning exposure also are prone to thunderstorms accompanied by high winds. It is for this reason that any lightning protection system should be properly anchored to the structure to avoid being dislodged by high winds. In the aftermath of a high wind event, it is not unusual to find that cables and components of lightning protection systems have broken loose from their anchorage points. The movement and impact of the lightning protection components, especially on membrane roofs, can lead to holes and cuts in the roof surface that lead to water intrusion.

While it is difficult to estimate the actual loads on the cables when they begin to move in strong winds, it is clear that installations with cables held in place with aluminum prongs on cleats are frequently inadequate in strong winds. Closed loop connectors are better suited for high wind regions. For additional guidance on securing a lighting protection system, see the Federal Emergency Management Agency’s Publication 549 – Rooftop Attachment of Lightning Protection Systems in High-Wind Regions.


Lightning can create strong electromagnetic fields, which can induce a power surge that affects power, telecommunications and radio frequency transmission lines; these in turn affect electric equipment inside a facility. Due to the low voltages normally used in data transmission cables and the sensitivity of the connected electronics, communications cables are extremely susceptible to induced voltage surges.

When lightning directly strikes exposed cables feeding electric equipment, the extremely large, overwhelming power surges it produces are devastating. State-of-the-art certified electrical surge protection systems are a part of the electrical systems of thousands of commercial and public facilities worldwide and are intended to maximize protection of life and property. The appropriate design and installation of the wiring within a facility is extremely important in mitigating the effects of surges.

Surge suppressors installed at the high exposure service entrances, where power enters the facility, establish the first line of defense against high powered, externally generated surges. These devices will address surges caused by lightning, power company grid switching, power system faults, severe weather, and neighboring facilities. If possible, use separate surge protection for office and circuits supporting electronic equipment and those supplying power to machinery and other equipment that may cause surges. Surge suppression devices should be installed in a staged, cascaded or layered manner to divert surges of various strengths at different points within an electrical system.

Install an Uninterruptible Power Supply (UPS) for computer equipment, which is an electrical apparatus that provides temporary emergency power when an input power source fails. Installing such a device for computers, data centers, telecommunications equipment or other electrical equipment could help avoid an unexpected power disruption that may lead to injuries, fatalities, serious business disruption or data loss. A UPS may provide approximately 10 to 20 minutes of power in order to allow personnel to save vital data and have a controlled shut down if long term back up power, such as a back-up generator, is not available.

Make sure the building’s electrical system is properly grounded in accordance with the National Electrical Code and that all telephone, cable and satellite wires are bonded to the same grounding point. Some equipment and circuits may require special attention. Process control, sensing and monitoring devices may all require individual protection, including plug-in units installed at point-of-use locations.

For information about additional layers of surge protection, visit the Lightning Section at http://disastersafety.org/.

For more information on protection of electrical systems and equipment, see FM Global Property Loss Prevention Data Sheets available in the Electrical Section at http://fmglobal.com.

© 2012 Insurance Institute for Business & Home Safety